An adjustable dockboard as disclosed in U.S. Pat. Nos. 3,203,002 and 3,528,118 includes a frame or supporting structure that is mounted in a shallow pit or depression in the loading dock. The conventional frame has a rear frame section and a forward frame section that are connected together by a series of stringers that extend in a fore and aft direction.
In the dockboard of the type described in the aforementioned patents, a ramp is hinged to the rear frame section and is adapted to be biased upwardly to an inclined position by a counterbalancing spring assembly. As disclosed in U.S. Pat. No. 3,528,118, the counterbalancing spring assembly includes a coil spring mounted within a tubular housing that extends in a fore and aft direction of the dockboard and the spring is connected to a lever arm secured to the rear edge of the ramp. The force of the spring, if unrestrained, serves to bias the ramp to an upwardly inclined position.
The ramp, when in the horizontal cross traffic position, should be flush with the upper surface of the dock so that the ramp will not interfere with the movement of traffic on the dock. When installing the dockboard in the pit in the loading dock, the dockboard is lowered by a hoist into the pit and the dockboard is shimmed to a level condition, in which the ramp is flush with the dock surface, by manually inserting shims under the frame. After leveling the dockboard, the shims are welded to the frame to support the dockboard in the level condition. The selection and positioning of the shims to level the dockboard in the pit is a difficult and time consuming operation.